Sounds very sensible. Too many parents think everyone should put up with their unruly kids (and the same goes for dog owners and their dogs, too).
Any child- and dog-free pub is likely to be me-friendly.
The only thing I would say is 12 is a little old, you only really need to ban under 7 year olds to get rid of the ones who run around and play Peppa Pig on loudspeaker.
Actually you just need to ban the parents, the kids would probably be ok if you told them the rules and the parents didn't think their kids were too good to comply.